[DaveNP]

I can't remember what I paid for the last set of jump leads I bought (recently to go in boot of wife's new car) but even for a good set they are not that expensive compared to a lot of motoring things, I'd echo the others buy good quality; you're already looking at heavy duty/high current, unless the connectors get so big they are impractical for a car then it's almost a case of you can't get them with too much current capacity (although the set we use for hgvs at work which almost need two hands to carry might be overkill for a car); I'd also look for longer leads, it saves the frustration of only being able to get so close and the batteries being on opposite sides of the cars; reasonable carrying case is nice as they should spend practically all of their life coiled up in the wheel well of the boot waiting to be easily unwound on the one occasion they're needed. If you buy local from a decent motor shop you can have a look at them before you part with the money.
Aluminium is a good conductor of electricity, overhead power lines are made of aluminium as it's a good compromise between weight, strength, conductivity and cost, makes me wonder if the jump leads are made of copper coated aluminium because we as consumers just expect electric wires to be copper.